The invention relates to a method for dealing with faults in an electrical drive system having an electrical machine and a pulse-controlled inverter, to an apparatus for driving a pulse-controlled inverter, and to an electrical drive system having an electrical machine and a pulse-controlled inverter.
Electrical machines having pulse-controlled inverters are used, for example, in hybrid vehicles, where they are operated selectively in motor or generator mode. In motor mode, the electrical machine generates an additional drive torque which assists the internal combustion engine, for example in an acceleration phase, and, in generator mode, said electrical machine generates electrical energy which is stored in an energy storage means, for example a battery or a supercap. The mode of operation and the power of the electrical machine are set by means of the pulse-controlled inverter.
Known pulse-controlled inverters comprise a series of switches with which the individual phases of the electrical machine are switched selectively to a high potential, the so-called intermediate circuit voltage, or to a low reference potential, in particular to earth. The switches are driven by an external controller which calculates a desired operating point for the electrical machine as a function of the driver input (acceleration or braking). The pulse-controlled inverter is connected to the controller and receives the relevant operating data and/or control commands from said controller.
In the event of a disturbance or a fault, for example when the battery current is too high or the feed current is too high, the pulse-controlled inverter is switched to a safe state in order to prevent possible damage to electrical components. In this case, different circuit states can be implemented in conventional methods.
In a first method, all the switches which are connected to the low potential, so-called low-side switches, are closed and all the switches which are connected to the high potential, so-called high-side switches, are open. This mode of operation is also called the short circuit state to low potential. In another disconnection method, all the switches of the pulse-controlled inverter are open. This is also called the free-running mode.
DE 10 2006 003 254 A1, for example, discloses a combination of these disconnection methods: since, for example, the phase current can still rise for a short time after the changeover to the short circuit state, said document proposes using the two known disconnection modes of operation sequentially and to switch the electrical machine initially to the free-running mode and then to the short circuit state.
DE 10 2007 020 509 A1 likewise proposes, in the event of a fault occurring in a drive system with a synchronous motor, a free-running mode initially being set and then a short circuit of the supply connections of the synchronous motor to earth being set, depending on the type of fault.
However, fault patterns in the case of which a short circuit to low potential does not represent a safe disconnection state of the electrical drive system or of the electrical machine, for example in the case of low-impedance defects in high-side switches in the pulse-controlled inverter, can occur in electrical drive systems. In such cases, a short circuit state to low potential would cause a short circuit of the supply voltage of the pulse-controlled inverter, and this can lead to further massive damage to the electrical drive system.
There is therefore a need for solutions which can ensure the safety and robustness of an electrical drive system in all fault situations.